Re: [PATCH v3 5/8] rebase: rename merge_base to branch_base

> 
> On Mon, Oct 17 2022, Phillip Wood wrote:
> 
>> On 17/10/2022 12:27, Ævar Arnfjörð Bjarmason wrote:
>>> On Mon, Oct 17 2022, Phillip Wood wrote:
>>>
>>>> On 13/10/2022 20:16, Ævar Arnfjörð Bjarmason wrote:
>>>>> On Thu, Oct 13 2022, Phillip Wood via GitGitGadget wrote:
>>>>>
>>>>>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>>>>>
>>>>>> merge_base is not a very descriptive name, the variable always holds
>>>>>> the merge-base of 'branch' and 'onto' which is commit at the base of
>>>>>> the branch being rebased so rename it to branch_base.
>>>>> To me "branch" means or has heavier implications of "named branch"
>>>>> than
>>>>> just a merge base, and this command is perfectly happy to work on
>>>>> commits disconnected from any named branch.
>>>>>> But more to the point, the rebase docs for --onto discuss a "merge
>>>>> base", so you'd read those, and then encounter this code talking about a
>>>>> "branch base", and wonder what the difference was...
>>>>
>>>> Aren't the docs saying the merge base is the base of the commits
>>>> (i.e. branch) being rebased? I don't think merge_base is a
>>>> particularly helpful name as it doesn't tell us what it is the merge
>>>> base of and branch_base was the best I could come up with. I see what
>>>> you mean in the detached HEAD case, but as the command also works with
>>>> named branches I hope it is fairly obvious what "branch_base" is in
>>>> the detached HEAD case.
>>> It *optionally* works with a <branch>, but doesn't require
>>> one. E.g. try
>>> this on git.git:
>>
>> Maybe I wasn't clear, I was referring to the fact that if HEAD isn't
>> detached then it rebases the current branch not about the optional
>> <branch> argument. I also think that the docs are for users, they are
>> not a guide to the code. With this change if you search for merge_base
>> in builtin/rebase.c you still find the part where we calculate the
>> merge base. This commit was added in response to a review comment from
>> Junio on V1, as far as I know he is happy with it and at this stage
>> I'm disinclined to change it.
> 
> I was mainly fishing for whether *you* grokked that it wasn't always a
> "merge base of a branch" in suggesting the rename. If you do & would
> like to keep this it's fine by me.

> Having said that.
> 
> I hadn't read the original discussion (or maybe I did, and
> forgot). Re-reading you're referring to the discussion ending at[1].
> 
> I think using "base commit" in this case (your other suggestion) would
> be better than either "merge base" or "branch base", just my 0.02.
> 
> In that case we could also use it consistently in our docs, and mention
> that (in some cases) it's the "merge base", and in others something we
> manually provide.
> 
> I agree that the docs are "not a guide to the code", and should not be
> required to keep the two in sync at all times.
> 
> But just do be clear I do think it's a strong signal that the code is
> being made more confusing if the variable that holds the "merge base"
> now (as discussed in those terms in the docs) is named "branch base",
> and we're seemingly unable (or at least I wasn't) to come up with a
> corresponding doc change that doesn't start sounding self-contradictory.
> 
> I.e. given that the whole point of 5/8 is to come up with a more
> descriptive name:
> 
> 	merge_base is not a very descriptive name, the variable always holds
> 	the merge-base of 'branch' and 'onto' which is commit at the base of
> 	the branch being rebased so rename it to branch_base.
> 
> Cheers.
> 
> 1. https://lore.kernel.org/git/c5b01472-7da9-6051-b127-1a8b8ddd2944@gmail.com/
> 
>>> 	git checkout origin/next
>>> 	touch f && git add f && git commit -m"file"
>>> 	git rebase --onto origin/master^{} HEAD~
>>> Here we transplant a commit on top of "next" to "master", without
>>> either
>>> of those *names* being involved, or their branches, just the
>>> corresponding OIDs/tips.
>>> That will go through e.g. can_fast_forward() which you're modifying
>>> here, and now populate a "branch_base" variable, instead of a
>>> "merge_base".
>>> I know that we conflate the meaning of "branch" somewhat, even in
>>> our
>>> own docs. E.g. we sometimes use "branch" and "named branch", but usually
>>> by "branch" we mean "named branch", and otherwise talk about a detached
>>> HEAD, <commit> or "tip".
>>> But in this case it's especially confusing in the post-image,
>>> because
>>> "git rebase --onto" explicitly uses an optional "<branch>" to
>>> distinguish the "named branch" case from the case where we're operating
>>> on detached a HEAD, or otherwise don't care about the "<branch>" (except
>>> as generic "restore us to where we were" behavior).
>>> So, if anything I'd think that we'd want something like this in
>>> various
>>> places in git-rebase.txt to make the distinction clearer:
>>> 	
>>> 	diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
>>> 	index 9cb8931c7ac..e4700a6e777 100644
>>> 	--- a/Documentation/git-rebase.txt
>>> 	+++ b/Documentation/git-rebase.txt
>>> 	@@ -18,7 +18,7 @@ DESCRIPTION
>>> 	 -----------
>>> 	 If `<branch>` is specified, `git rebase` will perform an automatic
>>> 	 `git switch <branch>` before doing anything else.  Otherwise
>>> 	-it remains on the current branch.
>>> 	+it remains on the current tip or named branch.
>>> 	
>>> 	 If `<upstream>` is not specified, the upstream configured in
>>> 	 `branch.<name>.remote` and `branch.<name>.merge` options will be used (see
>>> But your post-image seems to be to make this sort of thing
>>> explicitly
>>> more confusing, and e.g. these parts:
>>> 	@@ -206,8 +206,8 @@ OPTIONS
>>> 	 --onto <newbase>::
>>> 	 	Starting point at which to create the new commits. If the
>>> 	 	`--onto` option is not specified, the starting point is
>>> 	-	`<upstream>`.  May be any valid commit, and not just an
>>> 	-	existing branch name.
>>> 	+	`<upstream>`.  May be any valid commit, and not just an <-- this
>>> 	+	existing branch name. <--- this
>>> 	 +
>>> 	 As a special case, you may use "A\...B" as a shortcut for the
>>> 	 merge base of A and B if there is exactly one merge base. You can
>>> To sum up why I find this confusing: Reading this from the docs
>>> onwards
>>> I'd think (as is the case) that "<branch>" is optional. Then when I read
>>> the code I'd think a "branch_base" is something that *only* had to do
>>> with the "<branch>" case.
>>> But that's not the case, it's just a generic "merge base" in the
>>> same
>>> sense that "git merge-base" accepts all of these
>>> 	$ git merge-base origin/master origin/next
>>> 	d420dda0576340909c3faff364cfbd1485f70376
>>> (These two are equivalent, just demo'ing that we don't need the peel
>>> syntax):
>>> 	$ git merge-base $(git rev-parse origin/master) $(git
>>> rev-parse origin/next)
>>> 	d420dda0576340909c3faff364cfbd1485f70376
>>> 	$ git merge-base origin/master^{} origin/next^{}
>>> 	d420dda0576340909c3faff364cfbd1485f70376
>>> What *would* make things much clearer is e.g. calling a variable
>>> "branch_merge_base" *if* there is a case where that's a merge base only
>>> for named branches, but I don't know (and didn't look carefully enough)
>>> if you've got such a case or cases here. It just seems like a generic
>>> "merge-base".
>>>
>